i) Field of the Invention
The present invention relates to a method for producing a printing head of an ink jet printer, and more particularly to a method for producing an ink jet printing head for jetting ink particles by varying the volume of an ink chamber.
ii) Description of the Related Arts
As is well-known, an ink jet printer for performing printing by jetting ink particles onto paper is used as an output terminal of a computer and is mounted on a variety of electronic devices such as a word processor, a facsimile machine or the like.
In the ink jet printer, jetting of ink is carried out by an ink jet printing head (hereinafter referred to as a printing head).
In the printing head, conventionally, various ink jet systems have been proposed.
For example, as one ink jet system, a so-called Caesar system has been developed, as disclosed in U.S. Pat. No. 4,189,734.
In this system, an ink chamber is filled up with ink, and a piezoelectric element is provided near the ink chamber. By applying a pulse voltage to the piezoelectric element, the piezoelectric element is deformed to reduce the volume of the ink chamber. With this volume reduction of the ink chamber, the ink is jetted from an orifice connected to the ink chamber.
However, in a conventional ink jet system represented by the Caesar system, it is difficult to perform a high density printing due to a constructional restriction. Further, since there is a limitation to the shortening of the length of the ink chamber, fluid friction tends to increase, and thus it is difficult to use a high viscous ink in order to obtain high quality.
On the other hand, with the spread of ink jet printer, a low cost printing head has been desired. Hence, a method capable of simply producing a printing head with high reliability has been increasingly in demand.
Relating to the present patent application, one U.S. patent application of a new system printing head has been filed (Japanese Patent Application Serial No.Hei 3-242184 corresponding to U.S. Ser. No. 07/897,381, E.P.C. Serial No. 92110158.0, Korean Patent Serial No. 10833). In this printing head, high density printing and high printing quality can be carried out.
This printing head includes a piezoelectric block formed with a plurality of ink chambers (hereinafter referred to as ink "channels") which are filled up with ink, aligned in parallel and formed to pass through the piezoelectric block. A plurality of electrodes are formed on the internal walls of the ink channels, a front plate is mounted onto the front side of the piezoelectric block and a back plate is mounted onto the rear side of the piezoelectric block. In this case, a polarization treatment is performed to the whole piezoelectric block in advance.
When the printing is carried out by using this printing head, a voltage is applied to one pair of adjacent electrodes properly selected, and then the partition walls of the ink channels are deformed to change the volumes of the ink channels. Thus, with the volume changes of the ink channels, the ink is jetted from an orifice formed in the front plate to perform a dot printing on the paper.
Next, a general producing method of this printing head described in the above-described application will now be described.
First, a polarization processing to the piezoelectric block is performed. This polarization processing, for example, is carried out by holding the piezoelectric block between a pair of electrodes for the polarization processing and applying a high voltage between the pair of electrodes. By this operation, a polarization is caused in the piezoelectric block.
Then, a plurality of ink channels are formed in the piezoelectric block by using a laser beam processing technique or the like.
Next, a plurality of electrodes are formed on the internal walls of the ink channels of the piezoelectric block by using a light exposure technique, an etching technique or the like.
After these processes, a front plate having a plurality of orifices for jetting the ink and a back plate having one ink supply path is secured to the piezo-electric block to obtain an ink jet printing head. The ink supply path supplies each channel with ink.
In such a conventional ink jet printing head producing method, usually, the polarization processing is executed in a heated state of 100.degree. C. to 150.degree. C. by applying an electric field having a strength of 2 to 3 KV/mm for 20 to 60 minutes.
Accordingly, for instance, when the printing head is a small serial head having a width of 5 mm, the polarization processing can be carried out by applying a voltage of 2 KV/mm.times.5 mm=10 KV.
In turn, when the printing head is a large line head having a width of 220 mm, it is required to apply a voltage of 2 KV/mm.times.220 mm=440 KV.
Therefore, in case of a printing head having a large width, in particular, a high voltage polarization processing is required, and it is also necessary to deal with a surface current caused on the surface of the piezoelectric material. Hence, an ink jet printing head producing method capable of performing a polarization processing at a low voltage is desired.
Further, in the aforementioned conventional general producing method, it is possible that the polarization disappears during the ink channel formation step and the electrode formation step after the polarization processing. That is, due to the heat generation by the laser beam processing, there is the possibility that the polarized state becomes unstable.